The present invention relates to pneumatic tires for trucks and more particularly to means of preventing separation of ply turnup ends.
A pneumatic vehicle tire typically includes a pair of axially separated inextensible beads. A circumferentially disposed bead filler apex extends radially outward from each respective bead. At least one carcass ply extends between the two beads. The carcass ply has axially opposite end portions, each of which is turned up around a respective bead and secured thereto. Tread rubber and sidewall rubber is located axially and radially outward, respectively, of the carcass ply.
The bead area is one part of the tire that contributes a substantial amount to the rolling resistance of the tire, due to cyclical flexure which also leads to heat buildup. Under conditions of severe operation, as with truck tires, the flexure and heating in the bead region can be especially problematic, leading to separation of mutually adjacent components that have disparate properties such as the respective moduli of elasticity. In particular, the ply turnup ends are prone to separation from adjacent structural elements of the tire. More specifically, the ply is reinforced with materials such as nylon, polyester, rayon and metal which have much greater stiffness (i.e., modulus of elasticity) than does the adjacent rubber compound of which the bulk of the tire is made. The difference in elastic modulus of mutually adjacent tire elements leads to separation when the tire is stressed and deformed during use.
A variety of structural design approaches have been used to manage the separation of tire elements in the bead regions of tires. For example, one method has been to provide a xe2x80x9cflipperxe2x80x9d surrounding the bead and the bead filler. The flipper works as a spacer that keeps the ply from making direct contact with the inextensible beads, allowing some degree of relative motion between the ply, where it turns upward under the bead, and the respective beads. In this role as a spacer, the flipper reduces the inevitable disparities of strain on the ply and on the adjacent rubber components of the tire (e.g., the filler apex, the sidewall rubber, in the bead region, and the elastomeric portions of the ply itself).
The flipper is often made of a square woven cloth that is typically a textile in which each fiber, thread or cord has a generally round cross-section. When the flipper is cured in the tire, the stiffness of the fibers/cords becomes essentially the same in any direction within the plane of the textile flipper.
Examples of flippers are found in U.S. Pat. Nos. 2,489,614 and 3,253,693. The latter Patent also discloses data on radial and circumferential deformations within the tire. Such deformations result in shearing stresses during normal operation of the tire, but especially during severe operating conditions. Circumferentially directed shear deformations correlate with high shearing stresses within portions of the tire where the flippers overlap the radially oriented cords that reinforce the ply.
Also, given that the ply is, on each side of the tire, clamped around, or anchored to, or xe2x80x9cturned upxe2x80x9d about, the respective bead, there exists a xe2x80x9cturn-up endxe2x80x9d (as viewed in the cross section of a tire) that extends radially outward within, and circumferentially about, each sidewall. Limits on the length of the ply turnup ends are made in order to locate the ends of the ply in positions where radial deformations of the tire are relatively small. Generally the ends of the turnup ends of the ply do not extend beyond one third of the interior section height of the tire (i.e., the section height as measured from the nominal rim diameter to the inner diameter of the tire at its equatorial plane).
Stresses that result in the deposition of energy (i.e., the generation of heat) in the bead region and in the region where the turnup ends terminate are frequently accompanied by strains that contribute to separation failures at the turnup ends. A balanced design for a reinforced bead assembly of a tire has stress characteristics that lead to reduced flexural energy generation (heat buildup) and to strain characteristics that can be uniformly borne by mutually adjacent tire components in the bead region, including the turnup ends.
More particularly, radial-ply truck tires in which the one or more plies are reinforced with steel fibers or cords are prone to ply ending or turnup separation when exposed to severe service. Part of the cause of separation is related to the stresses described above and to the disparate moduli of elasticity of the respective metal and adjacent polymeric rubber compounds. As the tire undergoes flexure during heavy-duty use, flexure of the sidewalls in the region near to and immediately radially outward of the beads experience repeated flexural deformations in one or more directions, such as the radial and axial directions. Ply separation is especially problematic if the tire is overinflated or underinflated.
Prior to the use of steel-reinforced radial ply construction, the plies were reinforced with materials having substantially lower moduli of elasticity than that of steel. Accordingly, the stresses associated with heavy-duty tire use were more easily accommodated by the respectively adjacent components, such as the ply reinforcing materials and the adjacent rubber polymeric materials. (Such tires were, of course, less durable than are those having metal reinforced plies.) Still, disparities of respective moduli of elasticity could lead to ply separation under severe conditions, especially in region near the ply endings.
In addition to the use of flippers as a means by which to reduce the tendency of a ply to separate, another method that has been used involves the placement of xe2x80x9cchippers.xe2x80x9d A chipper is a circumferentially deployed metal or fabric layer that is disposed within the bead region in the portion of the tire where the bead fits onto the wheel rim. More specifically, the chipper lies inward of the wheel rim (i.e., toward the bead) and outward (i.e., radially outward, relative to the bead viewed in cross section) of the portion of the ply that turns upward around the bead. Chippers serve to stiffen, and increase the resistance to flexure, of the adjacent rubber material which itself is typically adjacent to the turnup ply endings.
Examples of patents of prior art uses of flippers and/or chippers are as follows:
U.S. Pat. No. 5,309,971 (Baker et al)
U.S. Pat. No. 4,667,722 (Klepper et al)
U.S. Pat. No. 4,462,448 (Kawaguchi et al)
U.S. Pat. No. 4,357,976 (Mezzanotte)
U.S. Pat. No. 4,289,184 (Motomura et al)
U.S. Pat. No. 4,047,551 (Mezzanotte)
U.S. Pat. No. 4,046,183 (Takahashi et al)
U.S. Pat. No. 4,024,901 (Pogue et al)
U.S. Pat. No. 3,638,705 (Devienne et al)
U.S. Pat. No. 3,028,903 (Lessig)
U.S. Pat. No. 2,958,360 (Mcacklem et al)
U.S. Pat. No. 2,902,273 (Lessig)
U.S. Pat. No. 2,501,372 (Benson)
U.S. Pat. No. 2,131,636 (Nellen)
U.S. Pat. No. 1,682,922 (McKone)
The U.S. Pat. No. 4,319,621 (Motomura et al) discloses several embodiments for use of an inventive metal chipper composed of a reinforcing element embedded in rubber and formed of 1 to 50 helically formed metal filaments. The FIG. 4d illustrates an embodiment using the metal chipper (43), constituted with reinforcing element (xcex2) composed of the helically formed filaments (6), as a flipper folded around the bead ring (2) from the inside to the outside thereof between the bead ring (2) and the carcass ply (3) and extended upwardly over the upper end of the turn-up portion (3xe2x80x2) of the carcass ply (3). A chafer (51) reinforced with conventional steel cords and chafers (52 and 53) each reinforced with nylon cords are further arranged outside the carcass ply (3), the turn-up portion (3xe2x80x2) of the carcass ply (3) and the metal chipper (43).
Each of these prior art patents can be distinguished from the present invention in that they do not include one or more of the features discussed below in the Description of the Preferred Embodiment of the present invention.
It is an object of the present invention to provide a bead region design that can reduce ply ending separation initiation and propagation within radial unisteel tires exposed to severe service conditions.
Generally, another object of the present invention is to reduce the flexural heat buildup associated with the cyclical shearing stresses and concomitant cyclical shearing strains in the bead regions of truck tires exposed to severe operating conditions.
Another object of the present invention is to employ a bead-region design feature, specifically the incorporation of a textile strip (i.e., a circumferentially disposed xe2x80x9cpatchxe2x80x9d) over both sides of the ply turnup ends and the radially outermost portions of the chipper so as to reduce deformation and shearing stress gradients and thus improve the tire""s overall resistance to initiation and propagation of ply ending separation in the bead region.
It is a further object of the present invention to incorporate in the bead region of truck tires a combination of chippers, active flippers and a textile xe2x80x9cpatchxe2x80x9d (circumferentially disposed axially outward of the ply turnup and the chipper) which operate in relation to one another in such a way as to provide spacers having such physical properties as modulus of elasticity which are intermediate between those of otherwise adjacent materials having significantly different moduli of elasticity (e.g., steel ply reinforcing wires/cords and rubber).
Yet another object of the present invention is to achieve the above objectives by means of the incorporation of a smaller number of components than are used in standard tire constructions wherein gum strips are applied at the radially outermost ply and chipper endings.
The present invention relates to a pneumatic radial ply tire having a tread, a carcass comprising a radial ply, a belt structure located between the tread and the radial ply, two inextensible beads, and two sidewalls. The ply is reinforced with a high-modulus material, and it is wrapped around the beads with its turnup ends extending radially outward beneath the sidewalls. Nylon fabric flippers are circumferentially disposed to between the beads from the wrapped ply, separating them from direct contact. Chippers made of steel cords are disposed circumferentially between the portion of the ply that wraps around the bead in the portion of the tire bead region that makes direct contact with the wheel rim when the tire is mounted. Nylon fabric patches are circumferentially disposed over the radially outermost reaches of the axially outwardmost parts of the chippers, the ply turnup ends and the flippers, overlapping the ends of each respective part.